1. Field of the Invention
The invention relates to a device for initiating a mechanical switching operation in synchronism with the breathing in inhalers having a membrane-like transmitter element.
2. Description of Related Art
Inhalers for administering inhaled preparations for therapy of the respiratory tract have been described in large numbers. In such devices, each actuation releases a specific dose of a pharmaceutical preparation. Depending on the type of device this preparation may be a micronised powder, an aqueous solution or a suspension of particles of the pharmaceutical (possibly a solution) in a liquified propellant gas. In any case, as the inhaler is actuated, an aerosol is produced from the pharmaceutical preparation. The production of the aerosol must be coordinated with the breathing so that the particles are well dispersed in the air breathed in and the particles reach the lower regions of the lung with the inspired air.
Some patients, particularly children and older people, frequently have difficulty in properly coordinating their breathing and the production of the aerosol.
To overcome these problems, various solutions have been proposed.
Apart from the possibility of initially spraying the aerosol into a container from which it is breathed in shortly afterwards (DE-A-2749629), the other devices have an apparatus which triggers the production of the aerosol in synchronism with the breathing, if the indrawn breath is sufficiently strong.
For an inhaler operated with propellant gas, DE-3040641 A1 describes a barrier which is supposed to be released by a sufficiently strong intake of breath at the mouth piece of the device, so that the aerosol can only be released when there is a strong enough suction produced by breathing in through the apparatus. However, there is a danger that the barrier will be jammed if the patient tries to trigger the jet of aerosol prematurely.
A propellant-free inhaler having the device described above for triggering a jet of aerosol in synchronism with the breathing is known from U.S. Pat. No. 3,921,637.
In the known inhaler, the transmitter element responding to the suction is a spring-balanced valve which is operatively connected via levers to a valve arrangement of the switching device. The valve arrangement is provided in the outlet line of a bellows pump which opens into a chamber containing capsules filled with the substance which is to be inhaled. The chamber in turn is connected to the outlet of the mouth piece.
When pressure is exerted manually on the pump bellows and the patient takes a strong breath inwards at the mouth piece, the valve responds to the suction produced in the mouth piece, moves forward and opens the valve via the levers in synchronism with the breathing. The pressure produced at the pump outlet generates a foreign air pulse which blows the dose of powder out of the capsule forming an aerosol which is then breathed in by the patient.
The known device has serious disadvantages. The transmitter device is of very complex construction and not easy to assemble. It consists of a plurality of very precisely machined components which have to be put together and adjusted in a complicated assembly process. Another serious disadvantage is the fact that the air breathed in flows through the inhaler and over the mechanical parts of the device. As a result, the depositing of dust and dirt on the precise bearings is unavoidable in the course of time. This may also occur, in particular, as a result of inhalers of this kind being carried in the patients' pockets. Any soiling of the delicate mechanical parts of the device may, however, call into question the operational reliability of such inhalers. However, devices of the kind described hereinbefore should present only slight resistance to the indrawn breath during inhalation. As a result, very little force is available for triggering the switching operation, and particularly the production of a foreign air pulse. Consequently, all the mechanical parts of the device are required to have an exceptionally easy action, which is not the case to the required degree in the known devices.
In view of the fact that the trigger means in known mechanisms operating with a spring bias required a sharp and almost abrupt flow of breath, DE-C 3901963 proposes a mechanical-electronic system. This system, however, requires a relatively high technical input and needs a current source.